The present invention relates to hydraulic antivibration supports, intended in particular for mounting the engine of a motor vehicle on the structure of the vehicle.
More particularly, the invention relates to a hydraulic antivibration support for interconnecting first and second rigid elements to damp vibration between said elements, the support comprising:
first and second rigid strength members for fixing respectively to the first and second rigid elements;
an elastomer body interconnecting the first and second strength members;
a hydraulic working chamber filled with liquid, and defined at least in part by the elastomer body; and
a flexible bellows of elastomer material defining at least part of a hydraulic compensation chamber filled with liquid which communicates with said working chamber via a constricted passage, said bellows presenting a central portion secured to a member carried by the second strength member and a periphery secured to said second strength member, and said bellows presenting a fold of generally annular shape centered on the central axis and projecting into the compensation chamber around said central portion of the bellows over a certain height up to a ridge of generally annular shape.
Document EP-A-0 939 243 describes an example of such an antivibration structure.
In known antivibration supports of that kind, the fold of generally annular formed by the bellows presents the advantage of making it possible to increase the scope for varying the volume of the compensation chamber.
Nevertheless, antivibration supports of that type suffer from the drawback of presenting a relatively high level of bellows stiffness, and in some cases that can impede free deformation of the compensation chamber and hinder the operation of the antivibration support.
A particular object of the present invention is to mitigate that drawback.
According to the invention, this is achieved by an antivibration support of the kind in question, wherein the fold presents a shape that is not circularly symmetrical about the central axis, and wherein the fold presents locally at least one depression having a concave side facing towards the compensation chamber.
By means of these dispositions, the fold is prevented from stiffening the bellows by an arching effect while the volume of the working chamber is increasing. This significantly reduces the stiffness of the bellows, and the performance of the antivibration support is improved.
In preferred embodiments of the method of the invention, one or more of the following dispositions may optionally be used:
said depression extends over substantially the full height of the fold;
the fold of the bellows extends angularly over a circular arc between two ends which are separated from each other by said depression that forms a non-folded zone of the bellows;
said depression is located in the ridge of the fold;
said depression is of a shape integrally molded with the bellows;
the antivibration support comprises at least one rigid bearing element secured to the second strength member and bearing locally on the fold so as to form said depression;
the bellows presents, in the ridge of the fold, a shape that is irregular, forming a succession of portions projecting towards the compensation chamber and of depressions each having a concave side that is open towards the compensation chamber;
the working chamber and the compensation chamber are separated from each other by a rigid partition having a central bore putting said working chamber into communication with an exciter member mounted to move perpendicularly to the rigid partition and controlled by a control device;
the exciter member is a flexible diaphragm having a first face which communicates with the working chamber via said central bore, and a second face which communicates with a pneumatic chamber having a coupling suitable for being connected to an external pneumatic source; and
the antivibration support includes a cover presenting an end wall and a peripheral wall secured to the second strength member and co-operating therewith to define a hollow inside space, said inside space containing a ring which connects the cover in sealed manner to the rigid partition around said central bore, the pneumatic chamber being defined between the flexible diaphragm and the end wall of the cover, the central portion of the bellows being secured to said ring, the compensation chamber being placed around said ring in the vicinity of the rigid partition, and an intermediate hydraulic chamber which communicates with said central bore being defined between the flexible diaphragm and said rigid ring.